Why limit access?
it prevents potential for accidental breakages or deliberate problems. You might give your fulfiment provider access only to the Order screen or a coder access only to the theme, settings, pages and collections but not your customer list.
How to give limited access to a staff member
First go into admin/settings/account
You will see a list of all the current users (or you can add a staff member).
Then click on person's name and choose the to limit acces, and pick you want to give them.
Easy! And much safer than giving everyone access to everything.